Dynamics: Newton's Second Law

In summary, the conversation discusses a problem involving a racecar covering a quarter mile track in 6.40 seconds and the driver's acceleration during this time. The first equation is used to solve for the "g's" and the second equation is used to solve for the horizontal force, with the correct answer being 2g or approximately 19.62m/s^2. The direction of the car's movement is important when setting up the equations.
  • #1
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Homework Statement


Here's the problem:
A particular racecarcan cover a quartermile track (402m) in 6.40s starting from standstill. Assuming that the acceleration is constant, how many "g's"(all i know is that it means accleration due to gravity) does the driver experience? If the combined mass of the driver and the racecar is 485kg, what horizontal force must the road exert on the tires?

Homework Equations


1. Δy(displacement) = [(Velocityinitial)(Δt)] + ((1/2)acceleration)(Δt)2
2. Forcegrav + (acceleration)(mass)= Forcetotal
I'm not even sure if the second equation even exists but that's what i made out from the problem.

The Attempt at a Solution


I tried solving for the "g's" using the first equation and i substituted the possible things:

402m = [(0m/s)(6.4s)] + [((1/2)a)(6.4s)]
i don't know if this is the right equation but its the closest that i can get

then i tried solving for the horizontal force with the second equation and substituted the given:
[(-9.8m/s2)(485kg)] + [(19.6m/s2)(485kg)] = Forcetotal

and in case oyu are wondering where i got the acceleration(19.6m/s2) its from the first equation i solved (which i think is wrong)

Thank you in Advance!

-yandereni
 
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  • #2
Hi, yandereni.

You did well in the first part. It looks correct.

yandereni said:
then i tried solving for the horizontal force with the second equation and substituted the given:
[(-9.8m/s2)(485kg)] + [(19.6m/s2)(485kg)] = Forcetotal
What are the directions of the two forces you've included here? What is the direction the question is concerned with?
 
  • #3
I
Bandersnatch said:
Hi, yandereni.

You did well in the first part. It looks correct.What are the directions of the two forces you've included here? What is the direction the question is concerned with?
Bandersnatch said:
Hi, yandereni.

You did well in the first part. It looks correct.What are the directions of the two forces you've included here? What is the direction the question is concerned with?
I looked at the problem again and there were no directions stated. And when i told my other classmates about the first part if i did it right, they said no and the answer should be 2.00m/s2.
 
  • #4
yandereni said:
I looked at the problem again and there were no directions stated.
what's this then, eh?
yandereni said:
what horizontal force must the road exert on the tires?

yandereni said:
when i told my other classmates about the first part if i did it right, they said no and the answer should be 2.00m/s2.
That's wrong. The car would cover some 41m at that acceleration.
 
  • #5
Maybe they meant 2g, not 2m/s^2?
2g is about 19.62m/s^2.
 
  • #6
oh, now i understand. but can i solve the horizontal force without any directions given?
 
  • #7
yandereni said:
without any directions given?
But you do know which direction the car is moving, don't you? All you need to make sure when setting up your equation is not to include forces that are not acting (i.e., have no component) in the direction you're interested in.
 
  • #8
Thank you very much! I got the right answer and i get the concept now. Thanks a lot! :)
 

1. What is Newton's Second Law of Motion?

Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. In simpler terms, this means that the more force applied to an object, the greater its acceleration will be, and the more mass an object has, the slower its acceleration will be.

2. How is Newton's Second Law mathematically represented?

The mathematical representation of Newton's Second Law is F = ma, where F represents the net force acting on an object, m represents the mass of the object, and a represents the acceleration of the object.

3. What is the relationship between force, mass, and acceleration according to Newton's Second Law?

According to Newton's Second Law, force, mass, and acceleration are directly related. This means that as force increases, acceleration also increases, and as mass increases, acceleration decreases.

4. How does Newton's Second Law apply to real-life situations?

Newton's Second Law can be seen in action in various real-life situations. For example, when a car accelerates, the engine applies a force to the car, causing it to accelerate. Similarly, when a person pushes a shopping cart, the force applied causes it to accelerate. This law also explains why it is harder to push a heavier object than a lighter one, as the heavier object has more mass and therefore requires more force to accelerate.

5. What are some common misconceptions about Newton's Second Law?

One common misconception about Newton's Second Law is that objects always move in the direction of the net force applied. However, this is not always the case, as other factors such as friction can also affect an object's motion. Another misconception is that the acceleration of an object is only dependent on the net force applied, when in reality, it also depends on the mass of the object.

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